1. Field of the Invention
The present invention relates to set activated aqueous cementitious compositions comprised of ultra fine particle size condensed silica fume and methods of using such compositions for well cementing.
2. Description of the Prior Art
Heretofore, hydraulic cement compositions have been utilized for carrying out a variety of cementing operations in oil, gas and water wells. Such compositions have typically included a particulate hydraulic cement such as Portland cement, water, and other additives such as dispersing agents, fluid loss control additives, set retarding additives, anti-strength retrogression additives and the like.
While such hydraulic cement compositions have been utilized successfully in carrying out a variety of well cementing operations, certain inherent problems and disadvantages are encountered in their use. For example, the particulate hydraulic cement must be mixed with the water utilized at the job site in that after mixing, the hydration reaction which results in the thickening and setting of the mixture quickly begins. This requires the presence of particulate solid and liquid mixing equipment at the job site and the use of the resulting cement composition within a relatively short period of time after mixing. In addition, while very fine particle size hydraulic cement has been used heretofore, aqueous slurries of such cement particles have still been unable to penetrate some very low permeability formations. Also, hydraulic cement slurries often have less than the desired thixotropic, flow, solid-suspension, corrosion resistance, low fluid loss and/or anti-strength retrogression properties without the addition of cost increasing additives thereto.
Thus, there is a need for set-activated cementitious compositions which can be utilized for carrying out well cementing operations which are relatively inexpensive, contain suspended particulate solids of extremely fine particle size, are comprised of premixed liquid components which can be stored at the job site until needed and then readily and easily mixed, have properties suitable for use over a wide range of well conditions, have excellent thixotropic, flow, solid-suspension, anti-strength retrogression, corrosion resistance and low fluid loss properties and contain little or no water soluble free lime.